Traditional optical via critical dimension (CD) measurements can be used in the manufacturing production line and measure the via diameter at the bottom (vb) and top (vt) of the via. If there is a large difference between top and bottom via CD value, then “chamfering” is occurring. It can also be detected when chamfering occurs using mid-via CD measurements, however, even with mid-via CD measurements it cannot be determined, how deep (vd) the chamfer is going inside the via, therefore how much process margin is there left. If at the measurement site the distance between via bottom and chamfer bottom are so small that at other parts the wafer chamfer reach all the way down to the metal below due to normal on-wafer local process variation, then the process margin can be considered insufficient.
Traditional cross sectional cuts (X-SEM, X-TEM) are able to provide a cross-sectional view of processed material, measuring all the dimensions (vt), (vb), (vd). However, this is a destructive method and cannot be applied in a production line to monitor functional semiconductor wafers.
It would be desirable to have a method of monitoring whether a significant amount of chamfering, with a large depth is occurring during manufacture of semiconductor wafers.